TaskMacCreadyTotal: add "pure" attributes
OrderedTask: fix indent
TaskSolution: fix indent
debian/rules: don't use "make clean"

Delete only this build's output folders.  Doesn't discard other
targets.
Makefile: re-add -I$(SRC) to WINDRESFLAGS

Necessary for including resource-launch.h.
release v6.7_beta2
Topography/TopographyStore: Don't ignore 100% opaque layers on non OpenGL targets
ExperimentalConfigPanel: fix "unused variable" warning
LanguageGlue: fix "unused function" warnings
ProfileKeys: remove obsolete variable "FLARMGaugeBearing"
VALI-XCS: remove unused variable "szInfo"
Task/Solvers: remove empty virtual destructors

Nobody ever deletes a pointer to one of these classes.
TaskSolveTravelled: fix indent
Task{EffectiveMacCrady,CruiseEfficiency}: add "virtual" and "override"
TaskSolveTravelled: make base class "protected"

No caller calls into ZeroFinder directly.
TaskSolveTravelled: protect time_error()
TaskSolveTravelled: make search() non-virtual
UnorderedTask: fix indent
TaskBestMc: fix indent
TaskBestMc: protect the base class